Help on poor mileage

Spoolin'Jim

Well-known member
Joined
Aug 23, 2006
Location
Appleton, Wi
TDI
2006.5 Jetta TDI, 5 speed, Pkg. 1, White
Hello everyone.

Back in November, my mileage went form a rock steady 52.x mpg to 44.x mpg and then worked its way down to 41.x mpg. I have kept records of every tank since buying the car new in August of 2006. It is a 06 Jetta TDI. Looking back, the lowest tank I had ever had prior was the very first tank, which was 48.2mpg. Ever since then it had jumped up 50-53mpg. Even when it was -20deg F, I was still averaging 48-49mpg. Now I’m struggling to get up to 42mpg. I had the dealer look at it and saw nothing wrong. Air filter is fairly new, brakes aren't dragging from what I can tell with it jacked up (though pads are worn at a strange angle but that’s a different question), tires are pumped up to 42psi (44 is max on sidewall), and I have tried several different brands of diesel and additives with no improvement. I tried unplugging the MAF and driving it and noticed no difference really in performance, and no difference at all at mileage. I’ve tried plugging the car in overnight so its warm from the start, and it still gets about the same as from 0deg F starts. The car is due for its 60k in 4k miles. I will have them change the fuel filter and air regardless unless I find out what the real problem is befor then. My driving habits have not changed in a way to degrade my mileage (if anything, I’m trying more desperately to get past 42 than before). The only thing that has changed has been the tires. I went from the stock Bridgestone's to Michelin Triple Treads back in early November, but the mileage decrease wasn't till the tank after they were put on. A 20% decrease seems a lot for a set of tires to do anyways. Does anyone have any insights as to where to look next? If it keeps its downward slide, I might trade it in. Yesterday it decided a bulb was bad, too, so I have that light on the dash despite not finding any burnt out bulbs. Also, the past few days, it seems like it has no power till about 1400rpm, where it then feels like someone flips a switch and it gets much peppier. It also takes 2-4 tries to start it in the morning (not plugged in and –15F). It wasn’t like that the past 2 winters at all. Even at –25F it cranked right up after 2 cycles of the glow plugs.

Okay, I think I’m done rambling! Thanks in advance!
 

ccvdubs

Vendor
Joined
May 23, 2008
Location
COLORADO
TDI
03 GOLF GLS
do your 60 k, have you done all maintenance including draining fuel filter? cold weather and winter fuel quality wiil drop fuel mileage. very normal
 

KROUT

persona non grata
Joined
Aug 26, 2005
Location
JAX FL
do you change the fuel filter every 20,000 miles. You should the 06's are very sensitive about bad fuel filters some wierd stuff starts to happen.
 

cp

Veteran Member
Joined
Jan 25, 2001
Location
usa
TDI
2006 TDI Beetle
A clogged filter isn't going to cause mileage to decrease. A clogged air filter might.

Do you notice any smell of diesel? Maybe you have a little leak.
 

40X40

Experienced
Joined
Feb 12, 2006
Location
Kansas City area, MO
TDI
2013 Passat SEL Premium
What has changed?
Tires. (ODO is now off in compared to the old tires)
Fuel. (Blend may be even more winterized)
Temps. (Colder now)
Traffic. (People drive different..)

Bill
 

KROUT

persona non grata
Joined
Aug 26, 2005
Location
JAX FL
cp said:
A clogged filter isn't going to cause mileage to decrease. A clogged air filter might.

Do you notice any smell of diesel? Maybe you have a little leak.
Have you driven a car with a clogged filter, especially a newer one. I had a customer that had one that was bucking and low power all due to the filter. So yes a clogged filter will affect mpg.
 

Spoolin'Jim

Well-known member
Joined
Aug 23, 2006
Location
Appleton, Wi
TDI
2006.5 Jetta TDI, 5 speed, Pkg. 1, White
I know its not the air filter that is glogged but cant vouch for the fuel or the fuel lfilter. The tires I put on changed my odomiter by 1% from what I had befor as verified by GPS and the road markers so the size difference didn't do 8-10mpg drop. I guess I will just go in for my 60k sooner than later and get the fuel filter changed. Needs it anyways I'm sure. Thanks for the sugestions.
 

Spoolin'Jim

Well-known member
Joined
Aug 23, 2006
Location
Appleton, Wi
TDI
2006.5 Jetta TDI, 5 speed, Pkg. 1, White
I know that colder temps and winter fuel affect mpg, but as stated in my first post, I have NEVER got below 48mpg on any tank, all city or all hwy. And when it started to go down to 42, it was still in the 40's here. Used to at 55mph, on a flat road, no wind, no nothing, I could pull upper 60mpg instantaneous mpg, not I get a whopping 50 or so. So something has changed. I don’t coast as far as I used to either. Trust me, I know my work commute like the back of my hand. Before November, I could always neutral coast from certain points to other certain points and now have to wait till over 100 feet further before I coast to make it. I thought brakes, but they don’t seem to be dragging. So if anyone has any actual ideas, please post them up and I will investigate, but don’t just use the generic "cold temps and winter fuel" unless you can prove that the winter fuel in Northern Wisconsin is blended differently than the past 2 winters in a way to affect my performance by 8-10mpg. I appreciate all the help, I'm just frustrated at my car and being told its nothing wont cut it.

James
 

KROUT

persona non grata
Joined
Aug 26, 2005
Location
JAX FL
Are you using the in dash mpg thing or are you doing by how many miles you drove divided by the amount of fuel you put in. I dont trust those in dash mpg things. The one in my truck is always off.
 

Spoolin'Jim

Well-known member
Joined
Aug 23, 2006
Location
Appleton, Wi
TDI
2006.5 Jetta TDI, 5 speed, Pkg. 1, White
I am using hand calculation. Aways done the same way. Fill till it hits the brim and let settle and repeat till no more can go in and divide miles on trip odom. by number of gallons used.


EDIT:

Looking around the forum, a few other people took larger than usual hits on mpg this winter as compared to the past as well. Fuel has no affect on my coasting distance however. Anyone know what all to check that will add drag besides the brakes, as mine seem fine to me and the dealer?
 
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eats1963

Veteran Member
Joined
May 7, 2007
Location
Saint Anne, IL
TDI
2015 Passat TDI SEL Premium
I've noticed that my MPG's dropped off from a consistent 51 MPG down to 47 MPG, and like you my driving habits have not changed. I'm assuming that this is due to the extremely cold weather this year compared to last.
 

cp

Veteran Member
Joined
Jan 25, 2001
Location
usa
TDI
2006 TDI Beetle
KROUT said:
Have you driven a car with a clogged filter, especially a newer one. I had a customer that had one that was bucking and low power all due to the filter. So yes a clogged filter will affect mpg.
You're correct. I should have said it won't have a negative effect on mileage, and a restricted filter can actually make mpg improve. All a restricted fuel filter can do is limit the amount of horsepower the engine can make. That's it. (If it gets too restricted, it can limit the amount of horsepower produced to -zero-.) At all other degrees of restriction, it simply limits the amount of power the engine can produce. Let's say a partially clogged filter can only flow enough fuel to make 50hp. Then the car can only go as fast as 50hp can propel it.

You are not going to get worse mileage by losing half the available horsepower of an engine. You'll simply accelerate and drive slower. It is like having an mpg-nutcase watching over the throttle for you. Very annoying, but you get good mileage.
 

KROUT

persona non grata
Joined
Aug 26, 2005
Location
JAX FL
cp said:
You're correct. I should have said it won't have a negative effect on mileage, and a restricted filter can actually make mpg improve. All a restricted fuel filter can do is limit the amount of horsepower the engine can make. That's it. (If it gets too restricted, it can limit the amount of horsepower produced to -zero-.) At all other degrees of restriction, it simply limits the amount of power the engine can produce. Let's say a partially clogged filter can only flow enough fuel to make 50hp. Then the car can only go as fast as 50hp can propel it.

You are not going to get worse mileage by losing half the available horsepower of an engine. You'll simply accelerate and drive slower. It is like having an mpg-nutcase watching over the throttle for you. Very annoying, but you get good mileage.
I will have to respectfully disagree with all of this.
 

KROUT

persona non grata
Joined
Aug 26, 2005
Location
JAX FL
How about you point out how a clogged fuel filter wont change the way the car runs. Have you ever driven a tdi with a bad filter. They will hesitate, surge and sometimes accelerate rough.
 

cp

Veteran Member
Joined
Jan 25, 2001
Location
usa
TDI
2006 TDI Beetle
I didn't say that a restricted filter wouldn't change the way a diesel runs. It does. Makes it run like it has less horsepower, because it does. To answer your question, no, I have not driven a TDI with a clogged filter, firstly because I've only owned one for two weeks and secondly because I don't let the fuel filters on my diesels get anywhere close to being used up. Now, anyway. I used to. I have experienced fuel filter clogging on many other diesels such as an '81 Rabbit, Case backhoes, and trucks with Cat, Detroit and Cummins diesel engines. In one old Kenworth truck I carried spare filters (it took two) with me at all times because it had an abnormal amount of junk in the fuel tanks. In every instance of a fuel filter clogging, it gave advance warning of impending walkage with a gradual, but smooth, reduction of power. In no case was it accompanied by any rough running, surging, missing, etc. Just a slow loss of power down to the point where idling isn't even possible. In most of these cases, the loss of power occurred at a time which caused the maximum possible inconvenience so I learned to not press my luck trying to get all of the advertised life out of fuel filters.

Now, if the TDI obeys some different set of rules than other diesel engines, I'd like to be enlightened.
 

KROUT

persona non grata
Joined
Aug 26, 2005
Location
JAX FL
leave yours on until its bad and maybe then you will believe me it does more than reduce power. Good luck.
 

cp

Veteran Member
Joined
Jan 25, 2001
Location
usa
TDI
2006 TDI Beetle
Could you not tell from my previous post that I *have* left them on to the point that the engine died??

You're going to have to explain what it is about a TDI that's different from every other diesel vehicle I have had that would cause it to behave differently.
 

KROUT

persona non grata
Joined
Aug 26, 2005
Location
JAX FL
what ever dude. I am done. I already explained it you seem to know more than I do. lol
 

Yaunick

Member
Joined
Jan 22, 2009
Location
Cortland, Ohio
TDI
2006 Jetta tdi A5 Platform
I have a 06 jetta with tdi pd and I have to agree with krout I Waited till 24 thousand to change my first fuel filter and I was on a trip home
whenever you would push the pedal above 3\4 ths the engine Would run eraddic and jump around, then when fuel demand went down it would run smooth, Man what a perforance Killer, I drove it 1000 miles Like that till i changed it.
I just Figured I will Have one as a Spare and the first hint of Trouble Change it. I got to 58 thousand and figured I'm Pushing my Luck and changed it again. It probably Wont hurt the engine unless you make it jerk around and add stress to gears and bearings. But i think if was running erradic while it was it might effect fuel Millage. On the other Hand other Diesel engines i've run Like detroit Diesel in 24 foot box truck did just loose Power. So Conclusion for Me is That The Tdi Does React different to Cloggeged Fuel Filter. Just my 2 cent worth
 
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Yaunick

Member
Joined
Jan 22, 2009
Location
Cortland, Ohio
TDI
2006 Jetta tdi A5 Platform
Just another Thought The Ecu In the Tdi Might Interpret Low Fuel Presure from the pump side of Filter Different than A mechanical Fuel pump would causing the jumping around and roughness.
 

velociT

Top Post Dawg
Joined
May 10, 2006
Location
Not Austin, TX
TDI
06 Jetta TDI *sold*
Mine also felt like it was cutting out at WOT right before the fuel filter completely plugged at 17k resulting in a no-start...

I'm doing 15k intervals on the fuel filter now.
 

diy_fool

Veteran Member
Joined
Aug 1, 2005
Location
Huntington, NY
TDI
'00 NB
Spoolin- I think you said it yourself:
"The only thing that has changed has been the tires. I went from the stock Bridgestone's to Michelin Triple Treads back in early November, but the mileage decrease wasn't till the tank after they were put on. "

It appears the rolling resistance is much higher on these tires so your coasting distance drops (and driving distance on the same quantity fuel as well).

I would suspect you just didn't catch it on the first fill up. Tires can make a big difference.
 

Railroad

New member
Joined
Feb 6, 2009
Location
Romsey, Hants. UK
TDI
Skoda Octavia Elegance
My TDi 110 averages 43.3mpg overall according to the trip computer. My wife drives it more than me, and she only does fairly short runs. Filling the tank brim-to-brim method also works out to be 43mpg, so I'm quite pleased that the trip computer does appear to be quite accurate. It runs very well and goes like a rocket. And it's very smooth to drive.

Some people claim that they get a regular 55+mpg from their TDi, but I never managed to get anywhere near this, although it will do 50mpg on a long run.

A mate of mine at work has a car the same as mine except that mine is an estate model and his is a saloon. His wife also mostly drives it doing fairly short runs, and he gets 8-10mpg more than me. I can't really figure out why mine is so much worse than his......
 

Spoolin'Jim

Well-known member
Joined
Aug 23, 2006
Location
Appleton, Wi
TDI
2006.5 Jetta TDI, 5 speed, Pkg. 1, White
Just a quick update. We had a few days that were in the 40's here and my mpg climbed up to close what it used to be. I'm sure some of that was the increase in tire pressure since I had them at 43 at 10deg F so it would have increased to roughly 46-47psi. So I'm holding out luck that warmer weather will help my cause. Too bad we still have lots more winter here in Wisconsin.
 

diesel4ever

Veteran Member
Joined
Sep 2, 2004
Location
Ontario
TDI
Golf 2000, black
I have had Triple Treads on my Golf and there was no drop in mileage when I put them on. It's a very good all around tire.
 
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